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/*!

    \example tools/styleplugin

    \title Style Plugin Example

    This example shows how to create a plugin that extends Qt with a new 

    GUI look and feel. 

    \image stylepluginexample.png

    On some platforms, the native style will prevent the button

    from having a red background. In this case, try to run the example

    in another style (e.g., plastique).

    A plugin in Qt is a class stored in a shared library that can be

    loaded by a QPluginLoader at run-time. When you create plugins in

    Qt, they either extend a Qt application or Qt itself. Writing a

    plugin that extends Qt itself is achieved by inheriting one of the

    plugin \l{Plugin Classes}{base classes}, reimplementing functions

    from that class, and adding a macro. In this example we extend Qt

    by adding a new GUI look and feel (i.e., making a new QStyle

    available). A high-level introduction to plugins is given in the

    plugin \l{How to Create Qt Plugins}{overview document}. 

    Plugins that provide new styles inherit the QStylePlugin base

    class. Style plugins are loaded by Qt and made available through

    QStyleFactory; we will look at this later. We have implemented \c

    SimpleStylePlugin, which provides \c SimpleStyle. The new style

    inherits QWindowsStyle and contributes to widget styling by

    drawing button backgrounds in red - not a major contribution, but

    it still makes a new style. We test the plugin with \c

    StyleWindow, in which we display a QPushButton.

    The \c SimpleStyle and \c StyleWindow classes do not contain any

    plugin specific functionality and their implementations are

    trivial; we will therefore leap past them and head on to the \c

    SimpleStylePlugin and the \c main() function. After we have looked

    at that, we examine the plugin's profile.

    \section1 SimpleStylePlugin Class Definition

    \c SimpleStylePlugin inherits QStylePlugin and is the plugin

    class. 

    \snippet examples/tools/styleplugin/plugin/simplestyleplugin.h 0

    \c keys() returns a list of style names that this plugin can

    create, while \c create() takes such a string and returns the

    QStyle corresponding to the key. Both functions are pure virtual

    functions reimplemented from QStylePlugin. When an application

    requests an instance of the \c SimpleStyle style, which this

    plugin creates, Qt will create it with this plugin.

    \section1 SimpleStylePlugin Class Implementation

    Here is the implementation of \c keys():

    \snippet examples/tools/styleplugin/plugin/simplestyleplugin.cpp 0

    Since this plugin only supports one style, we return a QStringList

    with the class name of that style.

    Here is the \c create() function:

    \snippet examples/tools/styleplugin/plugin/simplestyleplugin.cpp 1

    Note that the key for style plugins are case insensitive.

    The case sensitivity varies from plugin to plugin, so you need to

    check this when implementing new plugins.

    \section1 The \c main() function

    \snippet examples/tools/styleplugin/stylewindow/main.cpp 0

    Qt loads the available style plugins when the QApplication object

    is initialized. The QStyleFactory class knows about all styles and

    produces them with \l{QStyleFactory::}{create()} (it is a

    wrapper around all the style plugins).

    \section1 The Simple Style Plugin Profile

    The \c SimpleStylePlugin lives in its own directory and have

    its own profile:

    \snippet examples/tools/styleplugin/plugin/plugin.pro 0

    In the plugin profile we need to set the lib template as we are

    building a shared library instead of an executable. We must also

    set the config to plugin. We set the library to be stored in the

    styles folder under stylewindow because this is a path in which Qt

    will search for style plugins.

    \section1 Related articles and examples

    In addition to the plugin \l{How to Create Qt Plugins}{overview

    document}, we have other examples and articles that concern

    plugins.

    In the \l{Echo Plugin Example}{echo plugin example} we show how to

    implement plugins that extends Qt applications rather than Qt

    itself, which is the case with the style plugin of this example.

    The \l{Plug & Paint Example}{plug & paint} example shows how to

    implement a static plugin as well as being a more involved example

    on plugins that extend applications.

*/